This invention relates generally to air filters utilized in forced air streams and, more particularly, to the detection of debris trapped in the air filter for purposes of changing the air filter.
It is known that forced air filters are used to trap and remove undesirable debris and particles from a forced air stream. There are numerous applications and uses for such filtered forced air streams. A common use of a forced air stream includes conventional heating, air conditioning and ventilation (HVAC) systems utilized in residential and commercial buildings. Other similar applications or uses include providing controlled air supplies to particular rooms or confinements which contain activities such as manufacturing processes, assembling activities, electronic equipment and components which are sensitive to various air borne debris and need to be in a controlled air environment.
In the operation of these forced air streams, a filter is generally positioned in the path of the air stream contained in an enclosure, conduit or duct of an air system. The forced air stream carrying the debris strikes the filter on an upwind side of the filter and the filter traps the debris within its filter structure. The filter structure includes a porous medium which permits forced air through the filter and traps debris and particles. The porous medium often is pressed paper utilized in residential HVAC systems while polyester fibers are used in more commercial and industrial HVAC systems, however other common porous medium are used.
The trapped debris remains in the filter structure and the air stream passes through the filter and exits the filter on the downwind side absent the debris once carried by the forced air stream. As more air passes through the filter, more debris is trapped by the filter. As the filter becomes more burdened with the debris removed from the forced air stream, the filter becomes more blocked not permitting the air stream to readily pass through the filter as efficiently and effectively as it previously did with less debris trapped within the filter.
Typically the porous medium of the central portion of the filter receives the higher velocity and greater volume of air than the porous medium nearer the edges of the filter which are more proximate to the enclosure or conduit which contains the forced air stream. As a result, the central portion of the porous medium will tend to clog up and be blocked more quickly than the outer edges of the porous medium of the filter which receives less volume of air and therefore typically less debris.
A filter which is overly burdened with debris will cause back pressure on the air stream and will reduce the air supply to the desired destination of the air stream. Additionally, a more burdened filter is more likely to dislodge previously trapped debris and diminish the effectiveness of the filter. Thus, an overburdened air filter will diminish the air flow and at the same time, increase the debris content within the air stream downstream of the air filter. This will result in jeopardizing the comfort and health of the recipients or the operation of certain sensitive equipment and processes which receive such air stream.
As a result, the air filters that are in operation within the air stream must be monitored for replacement. This monitoring is typically accomplished by periodic visual inspection, and in other instances, the filters are merely automatically replaced at predetermined time intervals. Neither of these approaches are in response to the actual condition or debris content of the air filter. Additionally, the former is labor intensive and may require several visual inspections before replacement would be warranted. Moreover, the latter is somewhat arbitrary in that the forced air streams containing debris may vary over time in their content of debris and volume of air and therefore result in the filters being replaced either prematurely or too late.
The problems noted above are solved in accordance with the apparatus of the present invention which provides a device which provides an audible alert sound indicating the air filter has become overly burdened with debris thereby alerting the maintenance personnel to replace the overly burdened and ineffective air filter. The audible alert sound enables the maintenance personnel to replace the filter at a time when the blockage of the filter has actually occurred and alleviates time consuming periodic visual inspections or the inefficiencies created by arbitrary automatic replacement of the air filter at predetermined time intervals.
In accordance with the present invention a method is also provided to provide an audible alert sound to indicate to the maintenance personnel that the air filter is overly burdened with debris and needs replacement. This audible alert sound is provided at a time when the undesirable loading of the filter has actually occurred. The method enables the maintenance personnel to reduce the number of visual inspections and the time associated with such inspections. Additionally, the air filters can now be replaced at a time when the air filter is actually overly burdened and undesirably less effective for the subject air stream.